Preheat the oven to 180 degrees C. Brush eggplant slices with olive oil on both sides, and place them on a baking tray. Sprinkle garlic powder over the top. Bake for 10 minutes.
Heat two tablespoons of olive oil in a large frypan over medium heat. Add the onion, garlic, tomatoes and spinach. Cook and stir for a few minutes until fragrant, and the tomatoes have released their juices.
In a medium bowl, mix together the ricotta, 1/2 cup of the mozzarella cheese and 1/2 cup of the Parmesan cheese. Set aside.
Place the eggplant slices in a greased 20x30cm baking dish. Top with the spinach mixture. Spoon the cheese mixture over the spinach, and spread into a thin layer. Pour the pasta sauce over the cheese layer. Sprinkle the remaining mozzarella and Parmesan cheese over the top. Sprinkle with Italian seasoning.
Bake for 30 minutes in the preheated oven, or until heated through and the eggplant is easily pierced with a fork.